Purification of sand



Patented Dec. 4, I

PATENT OFFICE PURIFICATION OF SAND Theodore Earle, Denver, C010.

No Drawing.

Application September 19, 1932,

Serial No. 633,851. Renewed April 10, 1934 14 Claims.

My invention which I call my dry leaching process relates to a process which will remove small amounts of impurities such as iron oxide, alumina, manganese oxide, and the like from glass-sand, crushed feldspar and lepidolite, or other granular material, so that the ores or material may be made into more desirable products.

The object of my process is to reduce the amount of harmful ingredients in an ore or material such as the above and do this at a low cost both for chemicals, treatment, and equipment needed to handle the material.

In my former patent application, Serial Numher 511,446, filed January 26, 1931, I used dilute acid and brought this to the concentrated form by heating and evaporating the excess water in the diluent and thereby leavinga film of hot, concentrated acid around each sand grain to act on the impurities. v

The dissolved impurities are then washed free of the material. This process is even now in successful commercial operation but, from the cost standpoint, it has two drawbacks. Firstthe cost ofthe equipment andthe cost of the operation, because of the heat required in the evaporation of the e'xcesswater andSecondsince dilute sulphuric acid, for instance, vigorously attacks some materials, the entire equipment for this former process of mine must be planned and constructed to resist such attacks,

which adds greatly to the cost of the plant and equipment, and also adds to the cost of handling.

In my long study and many experiments along this general line, I have made what I believe to be an important discovery.

If, say; 1 to 10 pounds of water is mixed with a ton of dry sand, the first small fraction of the sand which contacts the water absorbs the entire 40 amount, leaving the balance of the ton of sand completely dry. This is about what anyone would naturally suppose to be the case. My surprising discovery is that if as low as one-half pound of concentrated sulphuric acid is properly mixed with a ton of dry sand, every particle and grain of the sand in the entire ton will be covered by a thin film of concentrated acid; in fact,

the result is just as certain, positive and valuable, as if the entire mass were first positively wetted with the dilute acid and the excess water then evaporated by heat, leaving the film of concentrated acid about each particle. If properly handled the mixing of the sand and small amount of acid can be done in a very short time,

with some sands in 30 seconds, and the acid will water.

be evenly distributed through the entire mass of sand.

The explanation of this fact is that concentrated sulphuric acid has very low cohesive power and high adhesive power as compared to This can be shown by putting a drop of acid and "a drop of water on a plate and then spreading these drops over the plate. The acid drop can be made to cover the entire surface of the plate, while the water drop covers only a small portion of the plate. performed before students of physics.

I am, therefore, taking advantage of my discovery in regard to sand and other granular materials irrespective of the size of the grain, and, in my present invention, my dry leaching process consists of properly mixing the desired small amount of concentrated sulphuric acid with the dry material and employing heat (which may be applied either before, during, or afterthe said mixing with the acid) to increase the activity of the acid in attacking the impurities of the material and subsequently removing, by washing or otherwise, the dissolved impurities.

Therefore, I am now, in this invention, going one step further than in my former invention, and am greatly reducing the cost of the necessary equipment and also the operating cost, and still I am accomplishing the desired object of removing those certain impurities from the sand grains, as will appear more in detail hereinafter. In the operation of this invention I am elimihating the cost of heating the sands or grains to the higher temperatures needed in the former invention, and the evaporation of the diluent.-

For most sands I now find I need only add the necessary "amount of concentrated sulphuric acid to the sand, which has already been dried, agitate or mix it until it is thoroughly mixed with the sand and then allow the mix to stand the necessary time and at the proper temperature, for the acid to act on the impurities.

By using concentrated sulphuric acid, I also, as stated above, do away with the extra cost of acid-proof equipment used in the former process (except in the final washing of the sand) and lower the cost of heating the sand to the much higher temperature formerly used. Sulphuric acid of B. or over does not attack iron and, consequently, equipment made of iron or steel can be used.

This new process will eifect an operating saving in most sands of between 10 cents to 15 This test is often cents per ton of sand and will lower the first cost of the plant over 60 per cent.

In the operation of present glass-sand cleaning plants the sand is brought as close as can be to grain size and as much of the dirt, clay, etc. is scrubbed off and washed away. After this cleaning the sand is put through driers, generally either of the Lewiston or rotary type, where the water is evaporated. As the sand comes from the driers it has a temperature of between 130 F. and 250 F. and is practically moisture free. It is then sent to storage bins for shipment.

My process, in its lowest cost form, passes this dry, hot sand, through a suitable type of mixer where the proper amount of concentrated sulphuric acid (the acid must be over 60 B. and should be the commercial 66 B. grade") is added to it.- By dry sand is meant a sand so free of moisture that no grains are held together with water and it will run freely as individual grains. The hot sand and acid are then thoroughly mixed. I have found by many tests on sands from all over the country that by properly agitating a mixture of dry sand with as low as one-half pound of concentrated sulphuric acid per ton of sand that the acid spreads over the grains and can be distributed so thoroughly throughout the mass that the iron film on all the sand grains is changed from the oxide to the water-soluble sulphate form and can be washed ofi. Of course, the heavier the iron film the more acid per ton is needed.- As much acid as is found necessary to clean the grains of any particular sand can be added to and mixed with the sand, but very few sands will need over 10pounds of acid per ton and none will need over 30 pounds per ton of sand to put the iron film into water-soluble form. Dry sand, or ore grains, and concentrated sulphuric acid will thoroughly mix in all proportions from one half pound of acid per ton of sand up to saturation. Any glass-sand with which I have tried this process will. still pour after being properly mixed with the necessary amount of concentrated acid. This is why I call it my dry leaching process.

After mixing the dry sand with the acid it is, in most cases, put in a bin or other receptacle where it is allowed to remain from 15 minutes to 48 hours. The acid acts much more rapidly on some sands than on others. With most sands this time of contact will vary between 4 and 24 hours. Time. of contact also varies with the temperature at which the sand is kept in the bin. The usual practice would be to deliver the sand to the mixer at a temperature between 150 F. and 250 F. This sand, after passing through the acid mixer should, for the best results, still have a temperature between 100 F. and 220 F. and should go to the bin within this temperature range. If the sand is too hot, that is over 250 F., a darkening of color may result because of the formation of water-insoluble sulphates. Keeping a temperature of over 212 F. for too long a time may result in this same darkening action, and some sands should not be kept at a temperature of over 200 F. If necessary, the sand can be kept at the correct temperature in the bin by the use of steam pipes or other proper means. If uniformly heated to the proper temperature before going to the bins, no extra heat should be needed. The action of the concentrated acid on'the iron film is extremely slow at temperatures ranging below-75 F. As the temperatures are increased up to the limits above described the needed length of time of contact between the acid and the sand rapidly decreases. As mentioned before,-the most efiicient range of temperature for the contact step and for the majority of sands ranges between 100 F. and 200 F. Below 100 F. the time of contact is too long for most sands and above 200 F. the chance of forming the dark waterinsoluble sulphates is present. However, temperatures to which more finely divided ores and other materials are to be treated depends upon the ore to be treated and the character of impurity to be removedtherefrom. But in no case should the temperature of the mixed ore and acid be raised above 560 F.

Concentrated sulphuric acid has the same spreading effect on the dry sand grains even though mixed with the sand at room temperatures. If it is mixed at these temperatures, however, the mixture should then be raised to the above described temperatures and kept at these temperatures for the above mentioned length of time to'get the desired results. The addition of heat greatly increases the action of the acid on the impurities and lowers the time of contact required in the bin.

After passing through the bin the acid-covered sand is given a thorough washing in water to rid it of the soluble iron, etc. compounds and remaining free acid. If necessary, a final, very dilute, alkaline wash may be given if the last vestige of free acid must be disposed of. After washing the sand it goes to the drier and is then ready for shipment.

The preliminary crushing, cleaning or desliming of the sand does not concern this process except that as much as possible of the impurities should be removed before adding acid so as to keep down the acid consumption. This cleaning is well done at present and the loose clay and the like, etc. readily removed. Nor does the treatment of the sand after the leach concern this process. Crushers, tables, magnetic machines, and all other equipment may or may not be used for the treatment preliminary to the leach or in the treatment after the leach. This process is only concerned with the removal of harmful impurities such as the iron oxide occurring as a film. around the individual sand grains. This film iron is, at present, either not being-removed at all or not being removed as cheaply or easily as is done by using the above described method. This-process can be added to and made a part of any of the processes of the present sand-cleaning plants. In the case of the'smaller grained ores and those that are more finely ground, enough acid should be added thereto so that all of the grains are completely covered therewith. The finer or smaller grains, the greater the total surface area to be covered with the acid. The amount of acid to be added must be sufficient to completely cover all of the surface area ofall of the grains and this quantity of acid will naturally increase with the fineness or smallness of the grains to be treated.

The discovery that an extremely small amount of concentrated sulphuric acid can be made, by proper agitation or mixing, to cover with a film of acid a very large number of separate dry grains of granular material appears to be new and no reference has anywhere been found bear-- ing on such action either alone or in connection with the leaching of glass sands.

Having now described my process, what I claim as new and desire to protect by Letters Patent, is as follows:

. 1. The herein described process of purifying dry sand or other granular mineral material comprising adding thereto concentrated sulphuric acid and thoroughly mixing the acid with the material, the amount of acid being sufiicient to cover all of the particles of the material with an acidfilm when said mixing is completed, but not sufficient in quantity to prevent the mixed material and acid from pouring substantially as if dry, and subsequently separating the material from the acid and the water soluble'compounds.

2. The herein described process of purifying dry sand comprising adding thereto concentrated sulphuric acid and thoroughly mixing the acid with the material, the amount of acid added being suflicient to cover all the particles of the material with an acid film when said mixing is completed, but not sufiicient in quantity to prevent the mixed material and acid from pouring substantially as if dry, and employing heat with a sand temperature not over 250 Fahrenheit to energize the action of the acid, and subsequently remove from the sand the acid and water soluble compounds.

3. The herein described process of purifying dry sand or other granular mineral material comprising adding thereto between one-half vpound and thirty pounds of concentrated sulphuric acid per ton and thoroughly mixing the sand and the acid, and subsequently removing the acid and water soluble compounds from the material. I q

4. The herein described process of purifying dry sand comprising adding thereto between one-half pound andthirty pounds of concentrated sulphuric acid per ton and thoroughly mixing the acid with the material, and employing heat until the material has a temperature of 250 Fahrenheit or less to energize the action of the acid, and subsequently removing the acid and water soluble compounds from the material.

5. Theherein described process of purifying dry sand and other granular mineral material .comprising adding to the material when at a temperature not above 250 Fahrenheit concentrated sulphuric acid, and thoroughly mixing the acid and the material, the amount of acid added being suflicient to cover all of the particles of the material with an acid film when the mixing is completed, but not suificient in quantity to prevent the mixed material and acid from pouring substantially as if dry, and subsequently removing the acid and water soluble compounds from the material.

.6. The herein described process of purifying dry sand or other granular mineral material comprising adding thereto concentrated sulphuric acid and thoroughly mixing the acid with the material, the amount of acid added being sufiicient'to cover all particles of the mamaterial with an acid film when said mixing is completed butnot sufiicient in quantity to prevent the mixed material and acid from pouring substantially as if dry, employing heat with the sand temperature not over 250 Fahrenheit to energize the action of the acid, storing the mixed acid and material while still heated for a contact period of time and removing the acid and water soluble compounds from the material.

8. The herein described'process of purifying dry sand or other granular mineral" material comprising adding thereto from one-half pound to thirty pounds of concentrated sulphuric acid per ton of material, thoroughly mixing the acid with the material, storing the material for a contact period of time and subsequently removing the acid and water soluble compounds from the material.

9. The herein described process of purifying dry sand comprising adding thereto from onehalf pound to thirty pounds per ton of concentrated sulphuric acid and thoroughly mixing the acid with the material, employing heat with the sand not over 250 Fahrenheit to energize the action of the acid, storing the mixed acid and material for a contact period of time and subsequently removing the acid and water soluble compounds from the material.

10. The herein described process of purifying sand or other granular mineral material comprising drying and heating the material and adding thereto from one-half pound to thirty pounds per ton of concentrated sulphuric acid and thoroughly mixing the acid with the material, storing the acid and the material for a determined period of time, washing the material free from acid and water soluble compounds and drying the material.

11. The herein described process of purifying sand and other granular mineral materials comprising drying and heating the sand and adding thereto concentrated sulphuric acid and thoroughly mixing the acid and the material, the amount of acid added being suflicient to form an acid film over all the particles of the material but not being suflicient in quantity to prevent the completely mixed material and acid from pouring substantia y as if dry, storing the mixed acid and materia while still heated for a determined period of time and washing the acid and water soluble compounds from the material and drying the material.

12. The herein described process of'purifying hot drysand or other granularmineral material comprising adding thereto concentrated sulphuric acid arid-thoroughly mixing the acid and the material, the amount of acid added being sufiicient to form an acid film about all the particles of the material when-the acid and material are completely mixed, but not sufficient in quantity to prevent the mixed acid and material from pouring substantially as if dry, storing the mixed acid and material for a determined period of time, water washing the material,

stantlally as if dry and subsequently removing the acid and water soluble compounds from the material.

14. The herein described process of purifyin dry sand and other granular material comprising adding thereto concentrated sulphuric acid and thoroughly mixing the acid with the ma terial, the amount of acid being sufficient to cover all the particles of the material with an acid THEODORE EARLE. 

